Conventionally, high heat resistance is required of an insulated wire for use in high temperature environment such as an engine room of an automobile. For this reason, as a covering material of the insulated wire for use in such a location, crosslinked polyvinylchloride and crosslinked polyethylene that are crosslinked in an electron irradiation crosslinking method, for example, are used.
Since reduction of a halogen-containing material such as polyvinyl chloride has recently been called for from the view point of reducing loads on the global environment, the halogen-containing material has been replaced with a material that contains no halogen element such as polyethylene. In order that the material that contains no halogen element may secure sufficient flame retardancy, a metal hydroxide such as a magnesium hydroxide is often added to the material as a flame retardant.
For example, PTL 1 discloses that a non-halogenous flame-retardant resin composition that includes polyolefin containing 30 to 80% by mass of a silane-crosslinking ethylene-vinyl acetate copolymer as an essential component, a metal hydroxide, and a flame-retardant auxiliary agent, the metal hydroxide content being 60 to 150 parts by mass and the flame-retardant auxiliary agent content being 5 to 10 parts by mass with respect to 100 parts by mass of the polyolefin is crosslinked to be used as a covering material of an insulated wire.